Molded lignocellulosic product



Patented June 2t, 1941 MOLDED LHGNOCELLULOSHC PRODUCT Arlie W. Schorgerand ."iohn iii. Ferguson, Madison. Wis, assignors to Burgess CelluloseCompany, lFreeport, llll., a corporation of Delaware No Drawing.Original application January 13,

1938, Serial No. 184,768.

Divided and this application September 12, 1938, Serial No. 229,526

Claims.

prior processes for making the plastic lignocellu lose products referredto above and products formed thereby, to render the products moreplastic, stronger and more water-resistant.

Briefly, the primary process consists in cooking a naturallignocellulosic material with water. alone or with added materials,within a limited range of temperatures and for a predetermined time torender water-soluble a part of the lignocellulosic material and toparticularly dissolve the hemicelluloses. after extraction of the watersolubles and subse quent drying, contains a large part of the originalthermoplastic resinous lignin, as well as cellulosic fibre intrinsicallyunchanged. This product may be hot-molded under pressure but without theaddition of a binder, into a hard, resinous product having a highstrength and a high resistance to the absorption of water.

The raw material for the process is any natural lignocellulosic materialsuch as wood, corn cobs. straw, bagasse. corn stalks, etc. When anatural lignocellulosic material is referred to herein it includesmanufactured products such as newsprint containing, for example,'70%-90% of coniferous ground wood. The ground wood therein issubstantially in its original or natural condition.

The lignocellulosic material, after being ground or otherwisecomminuted, is cooked at elevated temperatures with water, preferablycontaining a bufier, or a potential buffer, salt, or mixture of suchsalts, the purpose of which is to continuously neutralize the acidsproduced from the hydrolytic fission and at the same time form withthese acids other salts which act in a buffer capacity. Part of thehemicelluloses or other binding materials are thereby dissolved. The

time, temperature, and pressure used during the cooking operation mayvary within limits depending upon the' specific properties desired inthe final product.

Although water alone may be used during the cooking operation, a smallamount of buffers, or

The residual product,

active chemicals producing buffers, should be added during the cook toneutralize the acetic and other acids split off from the wood, andthereby form salts of these acids which further control the process bypreventing too much cellulose degradation, yet allowing hemicellulosehydrolysis. This is accomplished by adding basic chemicals to the cooksuch as lime, other alkaline earth hydroxides, calcium carbonate orother alkaline earth carbonates, alkali carbonates, alkali triphosphate, etc. The amount should be such that the cook is slightly acidat the end of the cooking operation, usually having a pH of 5.0 to 6.0.'If

more alkali is used than is necessary to neutralize the acid formed thelignin may be attacked thereby decreasing the amount of binder availablein the molding compound. Continuous neutralization during the cookingprocess is desirable to secure a well-flowed, water-resistant and strongproduct.

The cooking temperature and the cooking time are closely related insofaras the strength of the molded product is concerned. The presence ofmoisture in the molding compound during the molding operation affectsappreciably the properties of the molded product. The hydrogen ionconcentration during the molding operation also is a factor. If thewater absorption of the molded product is unimportant then cookingtemper atures (one hour cooking time) of from to 185 C. with hardwoodsawdust give the best results. In a specific instance a one hour cook at135 C. gave a product having its maximum strength when molded dry. Whenmolded moist the maximum strength resulted when the hardwood sawdust wascooked at a temperature of C. With the cooking time decreased to 15minutes and a cooking temperature of as high as 195 C. a molded productresulted which had excellent strength, though the maximum strengthresulted with material cooked at from C. to C. This product which hadbeen cooked 15 minutes, when molded dry had substantially greaterstrength than that which was molded moist.

The water absorption and extent of flow of the molded product appear tobe more closely related to the cooking temperatures and pressures than idoes its strength. Tests indicate that the maximum resistance tomoisture is developed when the cooking temperature, using hardwoodsawdust as the'lignocellulosic material, is from 180 C. to C. regardlessof whether the cooking time is 15 minutes or one hour though thesevariables in themselves afiect the water absorption.

For example, the moisture resistance of a moistmolded product decreasesrapidly as the cooking temperature decreases below 165 C. with a cooking time of one hour. If the same material is dry-molded the waterresistance is substantially less and decreases rapidly at cookingtemperatures below 165 C'. The same material cooked for 15 minutes andmoist-molded has an excellent water resistance when cooked attemperatures above 185 C. but at temperatures somewhat below thisdisintegrates upon being immersed in water for several days. Ifdry-molded this product exhibits less water resistance but greaterstrength. Cooking at above about 195 C. apparently affects the strengthadversely but improves the water resistance, though each naturallig'nocellulosic material has its particular characteristics, andvariations from the above data may be expected for the various rawmaterials. In general, it is usual to cook at 180 C. for 30 to 60minutes for optimum results.

During the cooking operation a part of the hemicelluloses and otherconstituents of the wood are dissolved. From 20% to 50% of the naturallignocelluioses are dissolved, 30% being about the average for wood.Corn cobs lose about 50% in weight on cooking at 185 C. for 1 hour;newsprint loses about 23% under the same conditions. and straw about44%.

After the cooking operation is completed the cooked product is washedwith water to remove substantially all of the parts renderedwatersoluble. The Wet pulp, which is dark brown in color, is then dried.When dried at 110 C. less than 1% of moisture remains, usually from0.50% to 0.75%. The dried product, called the primary material, isdisintegrated in a mill to a powder which should pass through at least a40-mesh screen and preferably a finer screen. The 6-5 mesh materialgives excellent results. Thus. when powdered it is in a form for use asa molding compound either alone or in combination with, for example,other organic materials. The primary material thus made consists of afiller and a binder. The filler is largely the cellulose of thelignocellu osic raw material. The binder is primarily the substanceresulting from the action of water on the lignin during the cookingoperation. Other fillers and binders may be added to the primarymaterial.

This molding-powder is plastic under hotmolding conditions and is wellsuited to molding operations. A sma l amount of moisture, usually 1.0%or more. present in the powder is advantagco us since the powder isrendered more plastic and the moisture resistance is increased ashereinbefore explained. The primary product may be molded at a pressureoi 1600 to 5000 pounds per square inch, a pressure of 3000 pounds beinga favorable one. while it is maintained at an elevated temperature,usually above 100 C. A favorable temperature is 185 (7., thou htemneratum of over 200 C. may be used. The moldina time should besu-fllcien't to roduce the desired hard and resinous properties, 2 to 15minutes usually sufficing for small obiects. The material is preferablymolded by giving it a preliminary cold press in the mold at hi hpressure, 6000 to 7000 pounds per square inch, and then drop ing thepressure. The mold is then heated. As the product heats the pressureagain rises. After being subjected to the desired pressure ashereinbefore specified for the necessary time, the mold may be cooledwhile maintaining some pressure. Hot or cold ejection is used.

The resultant product is hard, has a resinous appearance, remainsthermoplastic and has many of the properties of products made by moldingmixtures of a resin such as Bakelite and a filler such as wood flour.The moisture absorption is very low, for example, usually less than 2%when a 2 inch disk 5; inch in thickness is immersed in water for 18hours at room temperatures, The modulus of rupture varies with thedifferent materials. In a specific example it was 7000 pounds per squareinch when molded with a small amount of water and 8400 pounds per squareinch when molded dry. The density varied from 1.40 to 1.45. The bestresults are obtained if the hydrogen ion concentration of the primaryproduct is controlled during molding by the addition of a buffer such assodium acetate.

A small amount of zinc stearate, for example, 1%, may be mixed with themolding-powder to secure better release in the mold. The zinc stearateacts as a lubricant and also aids the water resistance.

Phenols or organic amines may be incorporated with the primary productbefore molding to increase the water resistance, plasticity and strengthof the molded product. The plasticity of the dried product isparticularly increased thereby. A mixture of a phenol and an organicamine appears to be more desirable than an equal amount of either onealone since the plasticity and strength are increased. Phenols which maybe used are phenol, nitrophenol, 0-, m-, and pcresol, alphaandbeta-naphthol, catechol, pyrogalloL- and p-aminophenol. Amines, bothaliphatic and aromatic, which may be used are aniline, dimethyl aniline,0-, m-, and p-toluidine, alphaand beta-naphthylamine,p-toluolsulphon-amide, phenyl ureas, proteins (zein, casein), butylamine, phenyl guanidine. The amount of these phenols and organic amineswhich may be used varies over a wide range, usually about 1% to 10% ofthe weight of the primary product being desirable.

Although water has been shown to be a desirable plasticlaer for theprimary product or primary plastic, we have found that oils of vegetableor mineral origin. such as pine oil, China-wood oil, castor oil, mineraloil, etc., will, when added to the dry primary plastic (dried to lessthan 1% moisture) in small proportions such as from to 7%, particularly1% to 3% produce a well flowed and complete molded product, without theuse of water, which is stronger and frequently more water resistant thanthe moist-molded product. Parafiin wax and other waxes such as montan,carnauba and Japan, in similar amounts also may be used. A mixture ofamines and oils is effective. The stearate does not seem necessary tosecure release when parafiin wax is used.

We have also discovered that by the use of 1--'!% of a mixture of cumarresin and an oil (such as those given above) in the proportion of 1:1 or1.25:0.75, an even better molded product results.

When water or other volatile (at the molding temperature) material isthe plasticizer, molding dlficulties may be encountered because thevolatiles must be permitted to escape. 'These volatiles can escape onlywith considerable difflculty in the larger molds and with greatdifliculty from wide boards or thick molded masses. It is apparent thatthe above-named plasticizers of low volatility in comparison with waterand alcohol previously used for this purpose, have a number ofadvantages which make for a superior and practical material.

The following table is given as illustrative:

Table Primary plastic is used throughout. In this case one cook was madein the usual manner usin CaCO as buffer and portions of this cook moi edwith the various plasticizers listed.

No'rn.ln every case the added plasticizers give stronger, better flowedand more water resistant articles.

Per cent gain after 24 hours complete immersion at room temperatures.

In the above description the primary lignocellulosic material is cookedin water, preferably buffered as described. The primary molding productthereby produced is somewhat deficient in plasticity and waterresistance. This deilciency may be overcome by raising the lignincontent of the primary product above the amount resulting from thatoccurring naturally in the lignocellulosic raw material in such a way asto insure a homogeneous lignin content. Although this increased lignincontent may be obtained-by mixing lignin produced separately to theprimary material we prefer to obtain this increase by using as thecooking liquor the so-called "blackliquors" of wood pulping processesnow used ex, tensively in the paper industry. These blackliquors arerich in dissolved ligneous materials which appear more reactivechemically when utilized in this way than those resulting from thehydmlytic action of strong mineral acids on lignocelluloses. Theligneous material obtained directly from alcoholic or alkalineextracting mediums are particularly desirable. The use of these liquorsdoes not entail any pro-purification before use and thereby obviates anypossibility of iignin degradation.

The black liquor, for example, from-the soda or sulfate process, 11' tooalkaline is neutralized to the desired pH (between 4-9) by means of anacid such as sulfuric acid, the lignin adjusted as desired by theaddition of water and the limo-- cellulosic material cooked therein asdescribed above, preferably in the presence 01' a buffer. If the blackliquor is neutral or acid, an alkaline material, such as calciumhydrate, may be added. Calcium carbonate also may be used. The lignin ofthe black liquor is thereby precipitated upon the naturallignocellulosic material. The dried primary product thereby produced hasthe necessary plasticity particularly if the pH of the cooklng liquor iscontrolled as previously described. An added plasticizer is not requiredalthough the water content is substantially lower than 1% (drying at 110C.). The primary product when hot-molded has excellent water resistanceand strength.

The amount of lignin added varies with the desired results, the amountof lignin in the lignocellulosic material to which it is added and uponthe source of the lignin. A smaller amount of lignin obtained from sodablack liquor appears to be as effective as a larger amount from sulfate'10 minutes. Cold ejection is used.

black liquor. For example, 10% of added lignin usually is efiective, butthe amount may vary over a wide range. Lignin obtained from a butanolcook seems to be as effective as that obtained from the sulfate process.The primary material containing the added lignin may be used for thoseproducts which are more difflcult to mold, that is, for those usuallyrequiring a material of high plasticity.

The primary product containing added lignins as described may beimproved as to plasticity and strength by the addition of oils and waxesas described.

Following are specific examples which illustrate practical embodimentsof our process so that those skilled in the art may practice it. Thetime of molding given is for articles about 0.10 to 0.20 inch thick. Theinvention is not limited to these specific examples.

(1) One part of maple sawdust is cooked with 1 part of water and 5% ofcalcium carbonate (of the weight of the air-dry sawdust) in an autoclaveat a temperature of 185 C. for one hour, the pilot the end oi the cookbeing about 5.5. The cooked material is filtered in a filter press andwashed with water until the water solubles are removed. The pH should bewithin the range 5.5-7.0. The filter cake is dried at C. to below 1%water. The dried material is divided into'three parts afterdistintegrating to a 100- mesh powder in a mill. (at) The first part ismixed with about 2% pine oil and 1% zinc stearate, introduced into acold mold and pressed at 7000 pounds per square inch. The pressure isthen dropped to about zero and the mold is then heated to 185 C. Thepressure in the mold is permitted to build up as a result of thetemperature rise to 3000 pounds per square inch for (b) The secondportion of powdered primary product is mixed with 2 per cent mineral oiland per cent zinc stearate, introduced cold into a mold and prepressedat 6000 pounds per square inch and the mold heated to C. for 10 minutesat this pressure after which it is cooled and the product ejected. (c)To the third portion 2 per cent of paraflln is added and the mixturepressed hot at 3300 pounds per square inch.

(2) One part of disintegrated corn cobs is cooked with 1 part of waterat a temperature of 185 C. for one hour in the presence of 5 per centsodium acetate as a buffer. The material is washed with water to a pH of5.06.0 and after substantially all of the water solubles are removed, isfiltered and then dried to less than 1 per cent H20. 5 per cent tung oilis then added. After being disintegrated to pass through a 65 meshscreen it is molded for 10 minutes at a temperature of 185 C. and at apressure of 5000 pounds per square inch.

(3) One part of maple sawdust is mixed with one part of sulfate blackliquor containing 10 per cent precipitable lignin, the alkali content ofwhich is neutralized to about pH 5.5-6.5, by means of sulfuric acid.Some brown lignin substances may gel in the liquor. The mixture iscooked for one hour at C. The pH should be between 5 and 5.5 at the endof the cook and preferably about 5.5.- The resulting solids are washedthoroughly, dried, and ground through 60 mesh. The resulting primaryproduct may be molded in the usual way with or without the addition ofoils or waxes. as set forth in the previous examples.

(4) One hundred fifty parts by weight of maple sawdust are mixed with 15parts by weight of aniline. With this is mixed a cooking liquorconsisting of 75 parts sulfate black liquor containing per centprecipitable lignin, '75 parts additional water and enough sulfuric acidto bring the pH to 0.0-7.0. The mixture is cooked at 180 C. for onehour. The resulting solids are washed free of solubles and dried at 110C. The mixture is molded hot after mixing it with 2% of Japan wax.

(5) The primary material of Example 1 after drying to 0.5% moisture ismixed with 2% pine oil and 2% aniline and molded at 185 C.

We claim:

1. In the preparation of a thermoplastic lignocellulosic material havingthe property of plastic flow underheat and pressure molding conditionsof 185 C. and 3000 pounds per square inch with formation of hard,water-resistant. resin-1ike products by cooking a naturallignocellulosic material with water at a temperature of approximately135 C. to 195 C. for approximately minutes to an hour in the presence ofan acidneutralizing agent in an amount such as to produce a pH ofapproximately 5.0 to 6.0 in the cooked mass at the end or" the cook todissolve a part of the hemicelluloses and render said natu-' rallignocellulosic material thermoplastic, leaching the cooked materialuntil substantially all of the water-solubles have been removed, dryingand reducing the leached material to a powder, the method of improvingthe plastic fiow of said product under heat and pressure moldingconditions which comprises adding to the dried material prior to themolding thereof, up to approximately 7% of a material from the groupconsisting of oils and waxes.

2. The method of claim material is an oil.

3. lhe method of claim 1 in which the added material is a wax.

4. The method of claim 1 in which the added material is paraffin wax.

5. The method of claim 1 in which the material is dried to less than 1%of moisture.

6. In the preparation of a thermoplastic lignol in which the addedcellulosic material having the property of plastic flow under heat andpressure molding conditions of 185 C. and 3000 pounds per square inchwith formation of hard, water-resistant, resin-like products by cookinga natural lignocellulosic material with water at a temperature ofapproximately 135 C, to 195 C. for approximately 15 minutes to an hourin the presence of an acidneutralizing agent in an amount such as toproduce a pH of approximately 5.0 to 6.0 in the cooked mass at the endof the cook to dissolve a part of the hemicelluloses and render saidnatural lignocellulosic material thermoplastic, leaching the cookedmaterial until substantially all of the water-solubles have beenremoved, drying and reducing the leached material to a powder, themethod of improving the plastic flow of said product under heat andpressure molding conditions which comprises adding to the dried material prior to the molding thereof, up to approximately 7% of a mixtureof tung oil and cumar IESlIl.

'7. A comminuted material having the property of plastic flow under heatand pressure molding conditions of 185 C. and 3000 pounds per squareinch with formation of hard, water-resistant, resin-like products,comprising a mixture of a treated natural lignocellulosic material andup to approximately 7% of a material from the group consisting of oilsand waxes, said treated natural lignocellulosic material beingsubstantially free of the water-solubles contained in a naturallignocellulosic material after being cooked with water at a temperatureof approximately C. to 195 (I, for approximately 15 minutes to an hourin the presence of an acid-neutralizing agent in an amount such as toproduce a pH of approximately 5.0 to 6.0 in the cooked mass at the endof the cook.

8. The comminuted material of claim 7 in which the added material is anoil.

9. The comminuted material of claim 7 in which the added material is awax.

10. A hard, water-resistant, resin-like, thermoplastic molded producthaving a density of approximately 1.40 to 1.45, comprising a compositlonof a treated natural lignocellulose and up to approximately 7% of amaterial from the group consisting of oils and waxes, said compositlonhaving the property of plastic flow under heat and pressure moldingconditions of C. and 3000 pounds per square inch, said treated naturallignocellulose being substantially free of the water-solubles containedin a natural lignocellulose after being cooked with water at atemperature of approximately 135 C. tol95 C. for approximately 15minutes to an hour in the presence of an acid-neutralizing agent in anamount such as to produce a pH of approximately 5.0 to 6.0 in the cookedmass at the end of the cook.

ARLIE W. SCHORGER. JOHN H. FERGUSON.

